Carriage bolts have a dome shaped head and a square neck, they are used mostly in wood construction like docks, and outdoor decks, etc... The square neck is designed to lock into the wood as the nut is tightened to prevent the bolt from turning.

Carriage Bolts are designed for use with Nuts and generally Washers, typically a Washer is not used on the head side as this prevents the square underside of the head from functioning properly.

All Carriage Bolts under 6" are fully threaded, lengths over 6" will always have 6" of thread.

Carriage Bolts are available in Grade 2/307A and Grade 5. Grade 2/307A Carriage Bolts are available in Zinc Plated and Hot Dipped Galvanized. Grade 5 Carriage Bolts are only available in Zinc Plated. Carriage Bolts are not available in Grade 8.

The true length of many bolts can commonly be up to 1/8" short of the stated length.

Carriage Bolt diameter is the width of the shaft or the outside of the threads.

carriage bolt chart

Carriage Bolt length is measured from the underside of the head to the end of the bolt, including the square underside.